Problems with PT100 NPT

Problems with PT100 NPT

Postby Iain_U1250 » Mon Mar 07, 2016 5:09 pm

I have a persistent problem with my Auber temperature gauge giving incorrect temperature readings. I have three Auber SLY 1813 gauges, one for EGT, one for engine water temp and one for the radiator temp. The EGT probe is a TC-KEGT, the engine water temp probe is a PT100A-NPT and the radiator temp sensor is a RTD-Auto.

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The gauges are fitted in my Unimog expedition truck. When I switch on the truck in the morning when it is cold (without starting) all three gauges should read the same temperature within a degree or two. The EGT and Radiator temp sensor always read the same, the engine water sensor however sometimes reads the same, sometimes 10-15 Deg C lower. Using a laser temp sensor, I have confirmed that the engine temperature as read by the EGT and radiator temp is correct, and that the PT100A sensor is giving a varying reading. I know I can offset this error, but I should not have to, given the sensor is supposed to be very accurate. I use this sensor to control the electric fans on the radiator, so it is very important to have this working properly. I can't tell whether the offset goes away at higher temperatures or not, and if I put an offset in to correct it when cold, I don't know if the error offset changes if I switch the truck off when hot, and I could be under-reading the engine temperature which will be very bad. Recently I fitted a mechanical thermoswitch for the fans to ensure I don't overheat the engine, but would prefer the Auber gauge to be accurate. I have checked the wiring, and it all seems OK,

I have swapped out the SLY 1813 gauge with some spare ones, and there is no difference, the offset is sometimes there, sometimes not.

This is the second PT100A sensor I have bought, the first would work for a while, then come up with an EEEE error occasionally so I bought a new sensor. Should I try a third PT100A sensor, or is there a more reliable sensor I can buy?
Iain_U1250
 
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Joined: Mon Mar 07, 2016 4:33 pm
Location: Australia

Re: Problems with PT100 NPT

Postby Sharron » Wed Mar 09, 2016 5:38 pm

Thanks for posting your question here.

The PT100A-NPT sensor has three wires, two red and one white. With this configuration, the gauge can measure the line resistance between two red wires (A), and measure the resistance between the white and red wires (B), subtract A from B then convert the resulted resistance value (B - A) to temperature. If there is something cause the gauge read a high line resistance (A), maybe due to loose connections, a bad crimp, or etc, then you will get a temperature reading lower than the real temperature value.

For this probe, you can check the cable connection. If you wiggle the wires or cable a little bit, does the reading change? Is the cable being pulled with some tension? You can also verify the temperature reading in ice/water mixture (stir 70% ice in 30% water) and in boiling water as well.

Please also contact customer service here. We can help you check if you still have any warranty on this probe.
Sharron
 
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Re: Problems with PT100 NPT

Postby jocklandjohn » Mon Dec 19, 2016 9:48 am

Thats odd Iain - I've had precisely the same problem. (in a Land Rover 100 exped camper)

I've the SYL2813 dual gauge with EGT on one channel and the water temp (out of engine into radiator) on the other reading via the PT100-NPT. I also have an analog gauge on the water temp out of radiator into engine with a thermostatic switch for the electric fan.

The Auber water gauge is ok most of the time. Then goes all over the place from 88 deg to 100 then to 150 and back down to 30 Deg. Often it will go offline completely with the EEEE message. Wiring has been checked and rechecked and all connections are ok. Curiously the thermo switch has never cut in to switch the fan on which suggests the probe readings are not accurate. I still have the original Land Rover dash gauge as well and it sits comfortably in the middle all the time so I've got enough confirmation of correct engine temp.

These were bought June 2015 and I'm wondering whether there is a bad batch perhaps? Or is it just that these are temperamental and VERY sensitive to wiring movement or engine vibration?

Will need to do some testing before buying a new on I think.

Whats the duration of the warranty period Sharron??
jocklandjohn
 
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Re: Problems with PT100 NPT

Postby Sharron » Wed Feb 08, 2017 1:51 pm

Hi jocklandjohn, sorry for the delay in reply you. From what you have described here, I guess it is the cable in the transition area (the section covered by the strain relief) that is about to break. Because of the vibration during driving, both the metal braiding outside the cable and the stainless steel housing for the sensor tip can wear out the insulation of the wires over time. You can remove the spring relief and check if any sign of wearing can be see in that area. The sensor carries 90 days warranty. Please contact tech support here.
Sharron
 
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Joined: Tue Sep 03, 2013 3:48 pm


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